Conventionally, there is well known heat treatment facility for castings and forgings of aluminum, steel or the like which performs a series of treatments, solution treatment, quenching treatment and ageing treatment.
For example, with regard to construction of facility shown in FIG. 9, plural work pieces (treated bodies) are housed in a tray 70, and each of the work pieces in the tray 70 is solution-treated, quenched and aged continuously while conveying the tray 70. Such an art concerning heat treatment process using the tray 70 is known.
With regard to the construction shown in FIG. 9, a reference numeral 71 designates a solution furnace, a reference numeral 72 designates a quenching bath, and a reference numeral 73 designates an ageing furnace. These members are supplied thereto with the trays 70 continuously. Conveyors 75 are provided in an underground pit 76 so as to recover core sand adhering to the work pieces. The conveyors 75 convey the core sand to a sand recovery box 77.
The Japanese Patent Laid Open Gazette 2003-183725 discloses construction that a solution furnace and an ageing furnace are rotary furnaces. With regard to this patent literature 1, a fast heat-up furnace is disposed which increases temperature in a short time before the solution treatment in the process of solution treatment, quenching treatment and ageing treatment. This fast heat-up aims to remove internal stress accumulated in the work pieces.
The construction of facility shown in FIG. 9 has below problems.
Firstly, at the time of heat-up in the solution furnace 71 and the ageing furnace 73, temperature distribution is uneven between the work pieces in the tray 70, and long time is required for all the work pieces in the tray 70 to reach to set temperature. As a result, the soaking time of the work piece with short heat-up time is long and the soaking time of the work piece with long heat-up time is short, whereby the quality of the work pieces becomes uneven. That is because the place that hot air cannot reach easily exists in the tray 70 housing the work pieces. For example, the quality of work pieces 78a and 78b shown in FIG. 10 is uneven.
At the time of cooling in the quenching bath 72, the cooling rate of the work pieces 78a and 78b is also uneven.
At the heat-up process and cooling process, heat energy moves concerning the heat-up and cooling of the trays 70, whereby the energy for the heat-up and cooling of the work pieces losses. Accordingly, the line of the solution furnace 71 and the ageing furnace 73 is extended and the output of burner is raised.
It is necessary to load the trays 70 to the facility and to take out the trays 70 from the facility.
It is conceivable to provide a fast heat-up zone at which the temperature is higher than the soaking temperature so as to shorten the heat-up time. However, because of the above-mentioned unevenness of the heat, some work pieces may be heated higher than the melting point.
The temperature in the solution furnace 71 or the ageing furnace 73 is fallen at the time that the tray 70 is conveyed into the furnace. That also causes the loss of energy and extends the heat-up time.
Since the tray 70 is cooled and heated repetitively, the tray 70 may be strained, whereby the tray 70 may be caught on a conveying way so as to stop the line. Furthermore, the maintenance cost of the tray 70 is required.
For recovering core sand, screws provided in chutes 79 so as to discharge the core sand on the conveyors 75, whereby a driving source for the screws is required. Furthermore, the screws are worn out by the core sand, thereby increasing the maintenance cost for repair or exchange.
Sand may fall at the connection point of the conveyors 75. For solving this problem, it may be constructed so that the conveyors 75 are omitted and the sand recovery box 77 is provided below each of the chutes 79. However, this construction increases the load for recovering the sand, thereby increasing the maintenance cost (labor cost).
The facility is constructed to convey the plural trays 70 therein, whereby the facility is large and number of actuators and the like of burners 81, fans 82 and conveying equipments 83 is increased. Accordingly, the execution cost is increased, the execution period is extended, and the maintenance cost is increased. Furthermore, the facility cannot be transferred and diverted easily.